This invention relates to microwave band frequency synthesizers.
In recent years, a microwave band frequency synthesizer of low phase noise has been used extensively in the field of satellite communications and the like. The microwave band frequency synthesizer of a three-loop construction is known as disclosed in, for example, DIGITAL PLL FREQUENCY SYNTHESIZERS' Theory and design by Ulrich L. Rohde, Ph. D., Sc. D.
The known three-loop frequency synthesizer, however, uses three phase-locking loops operating at different variable frequencies, thus requiring three kinds of voltage controlled oscillators (VCO's) used in the three phase-locking loops and in addition, it faces a problem that the spurious characteristics are difficult to maintain.